SPS (Semi-Persistent Scheduling) is a feature defined by the 3rd Generation Partnership Project that significantly reduces control channel overhead for QoS (Quality of Service) applications/services (VoLTE,VoiceoverLongTermEvolution) that require periodical radio resource allocations.
Procedures of semi-persistent scheduling and DCI formats are defined in 3GPP TS 36.213, Release 8, in which both SPS activation and release methods are specified.
According to the specification, the downlink SPS activation and release can be acknowledged by a communication device such as UE (User Equipment) through HARQ (Hybrid Automatic Repeat Request) feedback, such as ACK (acknowledgement)/NACK (negative acknowledgement) messages, on PUCCH (Physical Uplink Control Channel)/PUSCH (Physical Uplink Shared Channel), just like normal downlink dynamic scheduling.
According to the specification, uplink SPS activation can be also acknowledged through corresponding PUSCH transmission, just like normal UL dynamic scheduling.
However, as to uplink SPS release, 3GPP TS specifications just provide some constraints and do not specify a practical and effective procedure for both the notification and acknowledgment of uplink SPS release.